Simulation methods and apparatus are useful in increasing design productivity in a wide variety of applications because design defects can be detected prior to construction of the actual apparatus being simulated. Where the physical circuit or system includes an analog or mixed signal analog-digital component, simulation requires solving a system of simultaneous equations. The variables in these equations can be classified into one of several categories, depending on how their solutions are obtained. Input variables are variables whose values are effectively inputs to the system. Output variables are variables whose values are outputs of the system. Intermediate and system variables are variables that comprise the heart of the system, and whose values generally feedback on themselves.
In existing simulation systems, system variables exist in a one-to-one correspondence with some related equation; there is exactly one equation for each system variable slot. The relationship between a system variable and its related equation is determined prior to simulation and does not change during the simulation. Although this relationship is desirable, it is not always achievable. Occasionally one or more of the equations in the system of simultaneous equations are dynamic: i.e., the specific equation changes depending on specific circumstances of the system of simultaneous equations. Standard techniques for solving systems of simultaneous equations break down in the presence of simulation time changes in the relationship between equations and system variables.
Accordingly, a need exists for a technique for solving systems of simultaneous equations including conditional equations.